Chip cards mostly possess eight contact pads, five of which are typically used. They are the electric interface between, for example, a terminal and the controller of the chip card. One of these contact pads is a so-called I/O pad for communicating with external systems. Controllers typically also have at least one I/O pad for communicating with the exterior and are connected to the contact pad of the chip card. On modern safety controllers, there are at least two I/O pads, of which, however, typically only one is connected to the respective pad of the chip-card module. The second I/O port of the controller therefore generally remains unused in the final assembly.
In conventional safety controllers, it is very difficult to check which data actually reaches the exterior from the safety controller via an I/O pad. If the program flow of the safety controller is altered e. g. by an attack from the exterior, confidential data may unnoticeably reach the exterior. As a rule, attempts are made to protect the program flow by appropriate software counter-measures. These software counter-measures, however, provide limited protection only. In addition, a variety of sensors for detecting attacks are known. These detect a large proportion of the attacks, but also do not accomplish actual verification of the correct situation of the data output.